All-fiber ultrafast tunable thulium laser at 1.7 µm.

Area of Science:

• Laser Physics
• Nonlinear Optics
• Fiber Optics

Background:

• Ultrafast laser sources are crucial for nonlinear optical applications.
• Thulium-doped fiber lasers operating in the 1.7 µm region offer unique advantages for deep-tissue imaging and spectroscopy.
• Existing sources often lack tunability and high peak power in this spectral range.

Purpose of the Study:

• To present a fully fiberized, wavelength-tunable ultrafast thulium laser source.
• To achieve high-peak-power femtosecond pulse generation in the 1.7 µm spectral region.
• To demonstrate a compact and robust platform for tunable ultrafast laser generation.

Main Methods:

• A mode-locked oscillator with a carbon nanotube saturable absorber and a bending-induced short-pass filter in dispersion compensation fiber (DCF) was employed.
• Wavelength tuning was achieved by varying the DCF bending radius, enabling dispersion management and spectral shaping.
• Chirped-pulse amplification in a single-stage thulium-doped fiber amplifier with bi-directional pumping and a DCF filter was utilized.

Main Results:

• Continuous wavelength tuning from 1740 nm to 1860 nm was achieved.
• Stretched-pulse solitons were produced at the short-wavelength end of the tuning range.
• The system delivered 13.2 nJ pulses compressed to 366 fs, yielding peak powers over 36 kW.

Conclusions:

• A compact, fiberized, and wavelength-tunable ultrafast thulium laser source was successfully demonstrated.
• The laser system provides high-peak-power femtosecond pulses at 1.7 µm.
• This technology holds significant potential for applications such as deep-tissue multiphoton imaging and spectroscopy.